1. Field of the Invention
This invention relates to wall structures for buildings which can be designed to fail when exposed to internal pressures or external pressures exceeding selecting design values.
2. Description of the Prior Art
To protect buildings from excessive destruction, it is a design principle to provide exterior wall constructions which can be sacrificed to save the building framework when abnormally high pressures are developed, for example, explosions within the building; high winds outside the building; explosions outside the building; severe negative wind pressures outside the building.
Where external walls are double-skin construction, i.e., have an inner liner panel surface and an outer facing panel surface with thermal insulation therebetween, an accepted design procedure is described in U.S. Pat. No. 3,998,016 which describes a wall structure for single-span conditions and for double-span conditions. In each instance, the liner panels are secured rigidly to the building framework and have one end for each span which is releasably retained with the building framework. Corresponding facing sheets are secured by means of two different types of subgirts. The first type subgirt is connected to a previously fastened liner panel and to the building framework. The second type subgirt is connected only to a previously installed liner panel. This second type subgirt is spaced apart from the building framework by a predetermined distance which influences the failure threshold for the resulting wall. The facing panels, in these designs, have a one-to-one correspondence with the liner panels, i.e., if the liner panels are single-span, the corresponding facing panels are single-span; similarly if the liner panels are two-span, the facing panels are two-span.
A difficulty which has been encountered with the design of the wall construction of U.S. Pat. No. 3,998,016 is that the failure threshold differs for the wall span having an overlapped facing sheet and the wall span having an overlapping facing sheet. The described difference occurs because the upper span, of a two-span panel assembly, releases at its predicted release load whereas the lower span of the two-span assembly releases at a higher load because of the overlapping facing panel joint. This difference can be overcome by eliminating the panel release interference through the use of a redesigned overlapping joint involving a supplemental profiled filler piece. This technique proved effective but quite costly when actually installed in a building employing the panel design.